Vascular therapy uses minimally invasive, catheter-based procedures and specialized equipment and techniques. Catheters used in these procedures commonly employ a coating or liner on the inner wall to provide a smooth inner surface. A smooth inside diameter (ID) associated with these devices is beneficial in reducing friction against various catheter technologies such as stents, balloons, atherectomy or thrombectomy devices as they are pushed through the tight confines of the catheter lumen. If the catheter ID is not of sufficient lubricity, devices such as stents can cause damage to the liner as the devices are pushed through the catheter lumen. The effect of increased lubricity of the catheter ID is a reduced deployment force of catheter devices as they are passed through the lumen, increasing the likelihood of a successful procedure. The mechanical properties of a catheter liner are also extremely important. For example, high tensile and yield strength may be required when certain devices (e.g., flow diversion tubes, embolization, aneurysm bridging, scaffolding and thrombectomy devices) are passed through catheters in a compressed state. The compressed shape exerts an outward radial force, which causes friction with the ID, commonly making delivery of the device therethrough difficult. On the other hand, high flexibility of a liner is often desirable when catheters must pass through vasculature that involves sharp twist and turns (e.g., cerebral vasculature and below-the-knee (BTK) applications). In this situation, a highly flexible liner with intermediate tensile strength is often more desirable than a high tensile liner with low flexibility/high rigidity.
Various materials have been pursued as inner wall (base liner) materials for use, e.g., within such catheter devices. One material that has been considered is polytetrafluoroethylene (PTFE). PTFE is beneficial as it has a number of beneficial properties, including excellent chemical resistance, high temperature resistance, biocompatibility and very low coefficient of friction/high lubricity.
Known PTFE-based materials for use within catheter applications suffer from various drawbacks. For example, certain extruded PTFE tubes can be produced with sufficiently thin walls and sufficiently high tensile strengths, but exhibit high rigidities and high tensile modulus values, rendering them unsuitable, e.g., in applications where flexibility is important. See, e.g., U.S. Pat. No. 10,183,098 to Ohshika et al. Similarly, modified extruded PTFE tubes have been reported with high tensile strength, but undesirable stiffness, due to the method by which the high tensile strength was obtained. See U.S. Patent Application Publication No. 2015/0025562 to Dinh et al. Dip-coated and film-cast PTFE-based liners have been prepared from PTFE dispersion, and exhibit higher flexibility, but have rather low tensile strengths. Additionally, dip-coating methods are known to be cumbersome and suffer from low productivity (requiring repeated coating/sintering steps). Further, dip-coated tubes typically have relatively low abrasion resistance, as a result of separation of PTFE particles and, as such, the ID of these tubes often have inferior lubricity properties.
It would be beneficial to provide flexible PTFE-based tubes of sufficient strength and methods for preparing such tubes which render the materials suitable, e.g., for use in inner wall (base liner) applications.